The present invention relates to semiconductor packaging technology. The present invention has particular applicability to semiconductor packages containing multiple semiconductor dies and to wire bonding stacked dies to substrates.
Ongoing advances in solid-state electronic devices impose continuous demands for integrated circuit devices with increased functionality, density, and performance. In response, multi-chip modules have evolved comprising a printed circuit board substrate to which a series of separate components are directly attached. Multi-chip devices advantageously increase circuit density with attendant improvements in signal propagation speed and overall device weight.
A conventional method of effecting electrical connection between a die and electric leads comprises wire bonding. Wire bonding techniques effect electrical interconnections among components in a discreet package by means of fine wire connectors welded to the individual components. Accordingly, a fine wire conductor or bond wire has one end wire bonded to an electrical lead on the substrate surface and the other end wire bonded to an electrical contact or bond pad on the die or chip.
In fabricating conventional multi-chip modules or multi-chip packages, semiconductor dies are superimposed, with the upper die typically overlapping at least one side surface of the underlying die. Overlapping parts of the upper die extending beyond the side surfaces of the lower die contain bond pads on the upper surface to which bond wires are wire bonded.
For example, a conventional multi-die structure is schematically illustrated in FIGS. 1 and 2, wherein similar elements are denoted by similar reference numerals. Adverting to FIG. 1, substrate 10 has mounted thereon in a conventional manner first die 11 and second die 12 positioned above first die 1 such that overlapping portions 12A and 12B of second die 12 extend beyond or overlap the side surfaces of first die 11A and 11B, respectively. Bond pads 13 on the upper surface of first die 11 are electrically connected to conductor 16 on substrate 10 by wire bonds 15. Bond pads 14 on the upper surface of overlapping parts 12A and 12B of upper die 12 are connected to conductors 16 by wire bonds 15. Typically, the upper die 12 is positioned on first die 11 with a dielectric bonding material 20, such as an epoxy resin, therebetween, as shown in FIG. 2. Bond pad 14 on overlapping part 12A extending beyond the side surface 11A of underlying die 11 is wire bonded to a contact (not shown) on the main surface of substrate 10 with bond wire 15, as illustrated in FIG. 2. However, overlapping part 12A of upper die 12 is not supported on its underside. Accordingly, upon wire bonding bond wire 15 to bond pad 14 on the overlapping part 12A of upper die 12, cracking occurs in upper die 12, as indicated by arrow 21, with an attendant decrease in the durability of the resulting packaged semiconductor device and/or increase in rejection rate.
Accordingly, there exists a need for a semiconductor package comprising a circuit assembly with stacked, offset dies exhibiting improved reliability and structural integrity. There also exists a need for a method of manufacturing a packaged semiconductor device comprising a circuit assembly with stacked, offset dies with improved reliability and structural integrity.
An advantage of the present invention is a circuit assembly comprising offsetting stacked dies exhibiting improved reliability and structural integrity.
Another advantage of the present invention is a method of manufacturing a circuit assembly comprising stacked upper and lower dies without cracking of an overlapping portion of the upper die during wire bonding.
Additional advantages and features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a circuit assembly comprising: a substrate having a main surface; a first die having an upper surface, a lower surface and side surfaces, the lower surface of the first die positioned on the main surface of the substrate; a dielectric support material adjacent at least one side surface of the first die; a second die, having an upper surface and a lower surface, the second die positioned such that part of the second die is supported by the first die and another part of the second die overlaps a side surface of the first die and is supported by the dielectric support material; a bond pad on the upper surface of the second die on the overlapping part supported by the dielectric support material; and a bond wire connected to a conductor on the main surface of the substrate and wire bonded to the bond pad.
Another advantage of the present invention is a method of manufacturing a circuit assembly, the method comprising: providing a substrate having a main surface; positioning a first die having an upper surface, a lower surface and side surfaces, such that the lower surface of the first die is on the main surface of the substrate; dispensing a dielectric support material adjacent at least one side surface of the first die; positioning a second die, having an upper surface and a lower surface, such that part of the second die is supported by the first die and another part of the second die overlaps a side surface of the first die and is supported by the dielectric support material, the upper surface of the second die having a bond pad on the overlapping part supported by the dielectric material; and wire bonding a bond wire to the bond pad, the bond wire being connected to a conductor on the main surface of the substrate.
Embodiments of the present invention comprise dispensing a conventional molding compound or epoxy resin, conventionally employed in semiconductor packaging, as the dielectric support material. Embodiments of the present invention also include dispensing a molding compound or an epoxy resin on the upper surface of the first die extending along at least to opposing side surfaces of the first die and positioning the second die such that parts thereof overhang or extend beyond the two opposing side surfaces of the first die such that the overhanging parts of the second die are supported by the molding compound or epoxy resin. A plurality of bond wires are wire bonded to the bond pads on each of the overhanging or overlapping parts of the second die, the bond wires being connected to bond fingers or conductors on the main surface of the substrate.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive.